ELR-PPDU Design Considerations and Improvements in IEEE 802.11-24/1592r0 Document
Explore the design considerations for ELR-PPDU in IEEE 802.11-24/1592r0 document, addressing issues like SNR, false CRC passing, and coexistence with legacy standards. Learn about proposed improvements to enhance signal processing and classification for ELR devices, ensuring optimal performance and coexistence in wireless communication.
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September 2024 doc.: IEEE 802.11-24/1592r0 USIG fields in an ELR PPDU Date: 2024-09-09 Authors: Name Affiliations Address Phone email Hari Ram Balakrishnan Priyanka Bansal Rui Cao Rong Zhang Sudhir Srinivasa Hongyuan Zhang hariram.balakrishnan@nxp.com priyanka.bansal@nxp.com rui.cao_2@nxp.com rong.zhang_1@nxp.com sudhir.srinivasa@nxp.com hongyuan.zhang@nxp.com 350 Holger Way, San Jose, CA 95134 NXP 1 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 Introduction The following format was proposed for ELR-PPDU in [1]. Supports coexistence with legacy STA Legacy Preamble ELR Preamble ELR Data In [2, 3, 4, 5, 6], Various options on Legacy preamble in ELR PPDU have been discussed. The preferred option in all of them is the following: ELR- Preamble L-STF L-LTF L-SIG RL-SIG U-SIG-1 U-SIG-2 ELR Data U-SIG is present in most of the design proposals 2 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 Design Consideration The SNR design target [1, 7] of the ELR-PPDU is ~6 dB better than 11a/g 6 Mbps. The Legacy preamble does not have sufficient SNR for it to be decoded properly at the ELR STA at its range. U-SIG decoding of an ELR PPDU have high false CRC-PASS, i.e., a valid ELR PPDU at a ELR capable device being detected as a valid non-ELR PPDU. In this contribution, specific subfields in the USIG of ELR PPDU are defined which alleviate the false CRC passing issue for low SNR receivers, as well as enabling better coexistence and power save for high SNR receivers. 3 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 USIG content of an ELR PPDU Category Subfield Bit Pos Bits Value Category Subfield Bit Pos Bits Value PPDU type & Compression Mode 3 B0-B1 2 1 PHY Version identifier B0-B2 3 0 PPDU BW B3-B5 3 STA- ID value STA-ID B2-B12 11 UL/DL B6 1 - U-SIG-2 U-SIG-1 BSS color B7-B12 6 - 7 ELR validate bits B13-B15 3 TXOP B13-B19 7 - Disregard B20-B24 5 - CRC in U-SIG B16-B19 4 - Validate B25 1 - Tail in U-SIG B20-B25 6 0 Note: - means the value can vary and is Tx dependent PHY version Identifier: Set to 1 UHR format. U-SIG-1 is unchanged. 4 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 Potential Improvement for ELR devices In the case of a valid ELR PPDU received at an ELR device A considerable fraction of such PPDUs have the PHY version Identifier field flipped to non-UHR while the BSS color would still match, and the CRC would still PASS. In this situation, the following changes allow sufficient time for the receiver to process the legacy preamble portion till the ELR PPDU is detected. ELR validate bits (B13-B15) in USIG-2 set to all 1 s. ELR validate bits are set such that it they overlap with the Number of EHT/UHR-SIG symbols . When UHR-ELR PPDU is classified as non-ELR PPDU, ELR validate bits will be processed as Number of EHT/UHR-SIG symbols . Even if 2 bits are flipped with B13 = 1, the Number of EHT/UHR-SIG symbols 4 (minimum of 16us from USIG2), provides sufficient time to process and detect ELR PPDU. 5 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 ELR PPDU indication in USIG Field PPDU Type and Compression Mode 3 can be used to indicate ELR PPDU. Reuse a reserved (validate) value to indicate the ELR PPDU. 6 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 Enabling unintended nearby STAs to abort processing Unintended nearby STAs (both ELR & Non-ELR capable) should stop processing to prevent unnecessary power consumption. OBSS STA reception: BSS color can be used to stop further processing as non-ELR PPDU. InBSS STA reception: EHT/UHR non-ELR PPDU stopping criteria is through STA-ID. Version dependent fields in USIG can be repurposed in ELR-PPDU to carry STA-ID. InBSS STA reception: Phy version ID = 1 (UHR), BSS color matches, PPDU type & compression mode = 3 (ELR), and STA-ID not matching with USIG-CRC PASS. Any further processing can be stopped if the received PPDUs RSSI is good. 7 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 Summary In this contribution, we discuss how specific USIG subfields in an ELR PPDU can be set. Design philosophy: Provide sufficient legacy preamble processing time for ELR PPDU detection even when packet is classified as Non-ELR PPDU. Reuse a reserved (validate) value to indicate the ELR PPDU. Early termination based on STA-ID field. 8 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 Straw Poll Do you agree to define the USIG content of a UHR ELR PPDU as follows? Category Subfield Bit Pos Bits Category Subfield Bit Pos Bits PPDU type & Compression Mode B0-B1 2 Version identifier B0-B2 3 PPDU BW B3-B5 3 STA-ID B2-B12 11 UL/DL B6 1 U-SIG-2 U-SIG-1 BSS color B7-B12 6 TXOP B13-B19 7 ELR validate bits B13-B15 3 Disregard B20-B24 5 CRC in U-SIG Tail in U-SIG B16-B19 B20-B25 4 6 Validate B25 1 ELR PPDU indication: PPDU type & compression mode set to 11 . STA-ID (11 bit): B2-B12 bit in USIG-2. ELR validate bits (B13-B15 of USIG-2): Set to all 1 for ELR PPDU. Note: B11-B15 in EHT MU PPDU indicates Number of EHT-Sig symbols , and in UHR MU PPDU indicates Number of UHR-Sig symbols 9 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 Appendix: Potential Impact at ELR devices A valid ELR PPDU received at a ELR devices Considerable fraction of the PPDU has Phy version Identifier field flipped to non-UHR with matched BSS color along with CRC passing. The plot shows the probability that the packet is classified as non-UHR PPDU when receiving UHR-ELR-PPDU. Configuration: Ntx = 4, Nrx = 2, D channel, LSTF, LLTF boosted by 3 dB. Consider the following scenario: Phy version Identifier = x (~=1, decoded falsely), and number of EHT-SIG symbol = 1. Non-UHR device functionality: Operations related to EHT-STF will start after 4 us from USIG2. ELR PPDU is most likely not yet detected. 10 B Hari Ram (NXP) Submission
September 2024 doc.: IEEE 802.11-24/1592r0 References [1] 11-24-0873-02-00bn, Design Targets and Considerations for Enhanced Long Range , Jianhan Liu (Mediatek) [2] 11-24-1410-00-00bn, Legacy preamble for ELR PPDU , Ross Jian Yu (Huawei) [3] 11-24-1232-00-00bn, Discussions on Extended Long Range PPDU , Leonardo Lanante (Ofinno) [4] 11-24-1478-00-00bn, ELR PPDU design , Lin Yang (Qualcomm) [5] 11-24-1571-00-00bn, Extended Long Range (ELR) Mark Symbol Design , Rethna Pulikkoonattu (Broadcom Inc) [6] 11-24-1485-00-00bn, Considerations for ELR PPDU format , Dongguk Lim (LG Electronics) [7] 11-24-0875-01-00bn, UHR Enhanced Long Range Support , Rui Cao (NXP). 11 B Hari Ram (NXP) Submission
